Severe sepsis occurs in over 750,000 patients each year in the United States and is the leading cause of morbidity and mortality in critical care units. Activation of pro-inflammatory cells by bacterial products leads to a release of inflammatory mediators that induces the systemic inflammatory response of sepsis. The production of these mediators is regulated at the transcriptional level by enhancer elements nuclear factor kappaB(NF-kappaB) and activator protein-1 (AP-1) through interactions with specific kinases. In preliminary in vitro and in vivo studies we have obtained evidence that the systemic inflammatory response of sepsis may be counter-regulated by the nuclear reporter peroxisome proliferator activated receptor-gamma (PPARgamma). Pretreatment of macrophages with the specific PPARgamma ligands 15deoxy-delta12,14-PGJ2 (15d-PGJ2) or the thiazolidinedione troglitazone inhibits pro-inflammatory mediators induced by bacterial lipopolysaccharide (LPS) and heat killed Staphylococcus aureus (HK S. aureus). Consistent with this finding, we have found that PPARgamma ligands improve survival, reduce hemodynamic alterations, cytokine production and neutrophil infiltration in lung, colon and liver in rats subjected to septic shock induced by cecal ligation and puncture. Our central hypothesis is that the nuclear receptor PPARgamma is a critical anti-inflammatory pathway and that PPARgamma activation is beneficial in septic shock. Three interrelated specific aims will test this hypothesis. (1) We will evaluate the therapeutic efficacy of PPARgamma ligands on cardiovascular derangement and organ failure during polymicrobial sepsis in vivo. The effects of 15d-PGJ2, thiazolidinediones and nonthiazolidinedione PPARgamma ligands on septic sequelae will be examined in vivo in rats subjected to cecal ligation and puncture. (2) We will identify the molecular mechanisms of the actions of PPARgamma ligands in polymicrobial sepsis in vivo. The effect of PPARgamma ligands on nuclear activation of NF-kappaB and AP-1 and their regulatory kinases will be examined. (3) We will determine the role of cyclopentencne prostaglandins and PPARgamma in regulating cell signaling and inflammatory mediator production in macrophages/monocytes challenged in vitro with LPS and HK S. aureus. This approach will employ pharmacologic antagonists of PPARgamma and genetic manipulations with PPARgamma dominant/negative constructs and PPARgamma deficient macrophages from Cre-lox mice. The combination of in vivo and in vitro approaches will provide a strong test of the hypothesis that activation of PPARgamma is beneficial in sepsis.